Zircon and Apatite U‐Pb Constraints on the Tectonic Affinity and Metamorphic History of the Blueschist‐Facies Ambelakia Unit, Mt. Ossa, Greece

Abstract

AbstractIn the Aegean region, the Cycladic Blueschist Unit (CBU) and the Ambelakia unit (Mt. Ossa, Thessaly, Greece) represent early Cenozoic subduction‐related HP‐LT metamorphic complexes exhumed in the back‐arc of the Hellenic subduction zone. The Ambelakia unit has been linked to the classic CBU in the Cyclades; however, the tectonic affinity, structural position, nature of the protolith, or timing of metamorphism for these rocks in eastern Thessaly remains largely unresolved. This study provides detailed new insights into both the provenance, protolith age, and tectonic affinity of the Pelagonian, Ambelakia, and Olympos‐Ossa tectonic units by integrating U‐Pb detrital zircon (DZ) and detrital apatite (DA) data in a structural context. DZ results suggest the existence of distinct metasedimentary units, spanning in depositional age from Carboniferous to Late Cretaceous, with provenance signatures that support a correlation with the classic CBU and strengthen the argument for a similar pre‐subduction tectonic relationship. Depth‐profiling analysis reveals metamorphic rims that record HP‐LT metamorphism in the Ossa Ambelakia during the Paleocene‐Eocene. Apatite U‐Pb data from the metasedimentary units preserve a detrital signature similar to the DZ signatures, indicating that apatites were not reset (<450 C) nor recrystallized during subduction metamorphism. These new data suggest that the Ambelakia unit is a lateral equivalent of the CBU subduction complex; however, this unit experienced distinctly lower pressure and temperature conditions during metamorphism than the along‐strike classic CBU.